According to Google, its Google+ social network has 100 million active users a month less than two years into the service – even the largest skeptic should concede that the service has at least an outside chance of dethroning Facebook at some point (although that might not be its ultimate target, more on that at the end). Facebook’s new user numbers have leveled off a bit (which of course is a strong by-product of it approaching a billion users) so if Google+ continues to gain active users at a strong pace, it should continue to close that gap, very large as it may be.

That said, it isn’t going to be enough for Google+ to just continue to stay as it is to catch up with Facebook – the lead is too large, and hitting Facebook where it is strongest – for example, your real friends and family graph – isn’t going to cut it. Google+ needs to exploit Facebook’s weakest link and show that it will outpace Facebook at it for a long time. This is most likely the only way it will draw people away from using Facebook to using Google+ everyday. And that weakest link?

Mobile phones.

It isn’t breaking news to say that mobile is the future. Yes, people will still be using PCs – and seeing ads on them – for some time to come, but mobile – be it a smartphone, tablet or something in between (insert shout out to Galaxy Note fans), we’re not going out on a limb to say that mobile is where it will be at for the foreseeable future (i.e. the next five years – if you think you know what things will be like longer than that, stop reading this and start a company).

Since officially announcing that it was going public, Facebook has been pretty open about the fact that it agrees that mobile is the future, and although it has had a hard time monetizing its mobile apps, to Facebook’s credit it has taken strides to become a more mobile focused company. However, even with its improved apps, the acquisition of Instagram – which added to Facebook’s already very large mobile user base, although there is of course overlap – Facebook is still very vulnerable in mobile for one very clear reason: it doesn’t have its own mobile OS on hundreds of millions of phones like Google or Apple does.

This is a weakness that Google is extremely well positioned to attack Facebook on. While Facebook does have integration into the mobile OSs competing with Android (iOS and Windows Phone) it does not own Apple or Microsoft and as we’ve clearly seen with the Google Maps vs iOS Maps debacle, partnerships like that can only go so far. With Android and Google+, however, Google is the only company in the world that has both a very popular mobile OS and a popular-enough social network.

Google management has made no secret of its desire to integrate Google+ into all of its products (to the dismay of some) but when you consider that many of Google’s products are also very integral to Android (and in fact really make Android appealing to many) this strategy makes a lot of sense. On our PCs we really don’t need one click sharing of our Google Docs (sorry, Drive) to Google+ – it’s easy enough to copy and paste a link if we’re really all that bothered – but on the phone, where one click sharing and seamless integration is a must, the ability to link everything we do in with Google+ is a big, well, plus.

When Google+ launched less than a year and a half ago, its big pitch was that Circles was going to solve a problem that it felt existed – turns out, though, few people actually find sharing to be “broken” as the high number of Public posts on Google+ points to. Hard to blame Google for taking a shot at that angle – Circles was/is a pretty little UI thing, and there was a lot of angst against Facebook for all of the privacy issues, but most of that has died down now, and Circles is obviously just another way to organize contacts (and to a lesser degree content).

Turns out in fact, that Circles works best – guess where – on an Android handset. Organizing your contacts in Android 4+ using Circles is really nice, and the integration of everyone’s profile pics works really well. It’s the kind of thing that Facebook – if it had its own mobile OS – would probably be great at too, but without that level of OS integration, Google+Android (hey, that’s catchy…) is much more polished and useful.

Of course, neither Google+ nor Facebook are just contact lists that we can share links and status updates to. There are a ton of other features – most notably photo uploading and sharing – that both do well. Head-t0-head on a website-t0-website or mobile app-t0-mobile app basis, Google+ and Facebook stack up pretty much equally. Google+ has Hangouts, which is by far its best standalone feature, and Facebook has Facebook Pages which – even if you aren’t a brand or business – is really head-and-shoulders above what Google offers (i.e. users get deals, discounts, events, etc from vibrant communities that Google+ just doesn’t have).

Also, we aren’t saying that Facebook is by any means sitting on its hands – it’s rolling out new services regularly enough. However, without a homegrown OS to integrate into – that includes search, pics, maps, email, chat, docs, videos, translation, image upload and calendars to name just a few native features, never mind the 675,000+ Android apps available – all of Facebook’s features on a mobile phone seem boxed in (the reverse walled garden effect perhaps?) when compared to how Google+ is and can be integrated into Android.

If anything, Google needs to make this integration more prominent and push it harder to people that are looking to buy a smartphone. True, when you first set up your Android phone, Google prompts you about Google+, but it really needs to take a page out of Apple’s marketing playbook (ok, it should just take the whole playbook) and really play up the possibilities that a fully integrated mobile social network can provide.

The one thing that Google+ has sorely lacked since it launched has frankly been a soul – technically it makes a lot of sense, but it’s missing that emotional connection that will draw people into it and be absorbed enough to come there day after day, for hours at a time (i.e. what Facebook has been to many). Somehow, while there are hundreds of millions of Android phones in the pockets of the world’s population, Google hasn’t been able to forge that emotional bond between the phone and its connected users (that should be what Google+ is for), but if it can find that emotional glue, it could not only take down Facebook, but – and here is where we say what the ultimate target of Google+ is – arch-rival Apple.

If only Google had something coming that promises to take our most treasured experiences and show them to the world… if only Google+ could help us show the world what we see with our own eyes as we walk around and experience life… then Google would really be onto something, something that would be keeping Facebook and Apple execs up at night.